This invention relates to olefinic polymers grafted with a vinyl arylcyclobutene and to a method for preparing the arylcyclobutene grafted olefinic polymers, particularly a method for grafting a vinyl arylcyclobutene on an ethylene polymer.
Olefinic polymers, e.g., ethylene polymers, are employed to produce a variety of products such as blown film and in a wide variety of end use applications including blow molding applications. In many such applications and uses, it is desirable to improve the processability (e.g., more desirable flow characteristics during the processing of ethylene polymer). For example, it is known that long chain branching or lightly cross-linking an ethylene polymer will change its melt rheology and hence, flow characteristics. In addition, cross-linking an ethylene polymer has been shown to improve its creep resistance properties. Ethylene polymers are often cross-linked using a peroxide initiator. However, such cross-linking is not always desirable due to the formation of bubbles on the finished product due to decomposition of the peroxide, premature cross-linking and the interference of the cross-linking reaction by antioxidants which are also radical scavengers.
U.S. Pat. No. 4,622,375 describes the copolymerization of an .alpha.-monoolefin with an olefinic benzocyclobutene monomer of the formula: ##STR1## where R.sub.1 is hydrogen or CH.sub.3 and R.sub.2 is --CH.sub.2).sub.n where n is from 0 to 6. The copolymer is prepared using coordination catalysts of the Ziegler-Natta type conventionally employed in the preparation of linear low density and high density polyethylene. The resulting olefin/cyclobutene copolymers are cross-linkable. Unfortunately, cross-linking in such copolymers may occur prematurely. For example, the copolymer can be exposed to sufficiently high temperatures in the final processing steps following polymerization such as post-reactor devolitization to remove unreacted monomer to cause gel problems. In addition, it is difficult to accurately determine the amounts of the cyclobutene which is being incorporated within the copolymer.
In view of the stated deficiencies of the prior art, it remains desirable to provide an ethylene polymer which has or is capable of having long chain branching or light cross-linking.